There is proposed a contact intraocular pressure examination apparatus for measuring intraocular pressure by pressing a distal end of a probe pen against an eye, the probe pen holding a probe device including a vibrator for introducing vibration into the eye and a vibration detecting sensor for detecting the vibration reflected by the eye (see Patent Literature 1: JP2004-267299A).
Also proposed is a non-contact intraocular pressure measurement system for measuring intraocular pressure by making an ultrasonic wave enter in an eye (actually, an eyeball model) and detecting the ultrasonic wave reflected from the eye by use of a sensor (see Non-patent Literature 1: “Development of a new non-contact intraocular pressure measurement system using a phase shift method”, Masayuki JINDE and other three persons, Conference of Institute of Electrical Engineers, Sensors and Micromachines Division, Document p. 93-96, 2007). This system is arranged to measure a phase shift of a reflected wave with respect to a transmission wave as a frequency change, and determine a correlation between an amount of the frequency change and hardness of the eye model.
In the case of the apparatus configuration of Patent Literature 1, however, the probe pen is brought into contact with the eye to measure intraocular pressure and thus a large burden would be given to the eye. The apparatus configuration of Non-patent Literature 1 is merely intended to measure the eyeball model, which is insufficient to measure human eyes. In the case of measuring human eyes, which exhibit involuntary eye movement and visual line movement, the ultrasonic wave characteristics (e.g., frequency and phase) detected by the sensor are likely to vary due to misalignment of the apparatus with the eye, leading to variations in measurement results.